The following description includes information that may be useful in understanding the present invention. It is not an admission that any of the information provided herein is prior art or relevant to the presently claimed invention, or that any publication specifically or implicitly referenced is prior art.
Electroless metal deposition uses a redox reaction to deposit a layer of metals on a substrate without passage of an electric current. In this process, several types of metals can be used as catalysts for deposition of the metals. For example, palladium, platinum, silver, are well known catalysts for initiating electroless metal deposition on substrates. The catalysts facilitate initiation and subsequent deposition of electroless metals (e.g., copper, tin, etc.) from solutions of metal salts. The catalysts can be generated and deposited on a substrate in various forms (e.g., palladium can be deposited as colloidal palladium, ionic palladium, etc.).
Creation of metal patterns on various types of substrates is an essential part of electronic systems that are used in consumer products, communications, military, medical, and other industry segments. In order to make electronic systems more portable, mobile, functional, smaller, and less expensive, it is necessary to make a higher density, small sized circuitry, which requires new, cost effective pattern metallization processes.
Conventional fabrication of printed circuits uses a subtractive method of fabrication. To produce a desired copper pattern, subtractive processing uses a photolithography exposure and chemical etch to remove most of the copper that was laid down. Yet, such methods are expensive because it wastes a large portion of copper that is removed by etching steps, and is also time-consuming.
Many efforts have been put forth to create metal patterns using electroless metal deposition. For example, a printed circuit board can be generated by creating a negative resist pattern over the substrate surface, etching the surface, photosensitization and/or photo-desensitization, covering and/or stripping masks, and so on. U.S. Pat. No. 3,775,121 to Sharp discloses a method of deactivating of catalytic species deposited on the surface, and selectively reactivating a portion of the deactivated catalytic species using ultraviolet (UV) radiation. Similarly, U.S. Pat. No. 8,110,254 to Sharma et al discloses a method of creating a circuit pattern by decomposing catalytic precursor using electromagnetic radiation and energy (e.g., thermal energy, laser, UV heaters, ion beams, e-beams, etc.) on the substrate and/or palladium precursor.
In another example, U.S. Pat. No. 3,791,340 to Ferrara discloses a method of a depositing a metal pattern on a surface by photo-deactivating the catalytic species using some type of UV radiation. In Ferrara, some portions of the surface are covered with a mask that protects the catalytic species under the mask from being deactivated. U.S. Pat. No. 8,628,818 to Sharma et al. also discloses a method of creating a circuit pattern by using a printed, removable mask over precursor according to negative of desired pattern.
However, those methods may not be used effectively for catalysts that are not easily imageable to allow selective metallization in the form of an image. In addition, many of those methods require multiple steps that increase the complexity and cost of fabrication. Thus, there is still a need for an improved methods and systems for patterning electroless metals on a substrate.